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    Subject[PATCH 5/5] xen/time: add pvclock_clocksource_vread support
    Date
    Add support to register pvclock_vcpu_time_info structures in the userspace
    mapped page and set the xen clocksource .vread method if that works.
    The common pvclock code does everything else.

    Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    ---
    arch/x86/xen/Kconfig | 6 +++++
    arch/x86/xen/mmu.c | 3 +-
    arch/x86/xen/smp.c | 2 +
    arch/x86/xen/time.c | 52 ++++++++++++++++++++++++++++++++++++++++++
    arch/x86/xen/xen-ops.h | 8 ++++++
    include/xen/interface/vcpu.h | 41 +++++++++++++++++++++++++++++++++
    6 files changed, 111 insertions(+), 1 deletions(-)

    diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
    index b83e119..a002004 100644
    --- a/arch/x86/xen/Kconfig
    +++ b/arch/x86/xen/Kconfig
    @@ -13,6 +13,11 @@ config XEN
    kernel to boot in a paravirtualized environment under the
    Xen hypervisor.

    +config XEN_TIME_VSYSCALL
    + def_bool y
    + depends on PREEMPT_NOTIFIERS
    + select PARAVIRT_CLOCK_VSYSCALL
    +
    config XEN_MAX_DOMAIN_MEMORY
    int "Maximum allowed size of a domain in gigabytes"
    default 8 if X86_32
    @@ -36,3 +41,4 @@ config XEN_DEBUG_FS
    help
    Enable statistics output and various tuning options in debugfs.
    Enabling this option may incur a significant performance overhead.
    +
    diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
    index 4ceb285..99b8aa5 100644
    --- a/arch/x86/xen/mmu.c
    +++ b/arch/x86/xen/mmu.c
    @@ -1814,6 +1814,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
    # endif
    #else
    case VSYSCALL_LAST_PAGE ... VSYSCALL_FIRST_PAGE:
    + case FIX_PVCLOCK_TIME_INFO:
    #endif
    #ifdef CONFIG_X86_LOCAL_APIC
    case FIX_APIC_BASE: /* maps dummy local APIC */
    @@ -1834,7 +1835,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
    #ifdef CONFIG_X86_64
    /* Replicate changes to map the vsyscall page into the user
    pagetable vsyscall mapping. */
    - if (idx >= VSYSCALL_LAST_PAGE && idx <= VSYSCALL_FIRST_PAGE) {
    + if (user_fixmap(idx)) {
    unsigned long vaddr = __fix_to_virt(idx);
    set_pte_vaddr_pud(level3_user_vsyscall, vaddr, pte);
    }
    diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
    index 429834e..a2ee882 100644
    --- a/arch/x86/xen/smp.c
    +++ b/arch/x86/xen/smp.c
    @@ -313,6 +313,8 @@ static int __cpuinit xen_cpu_up(unsigned int cpu)
    if (rc)
    return rc;

    + xen_setup_vcpu_vsyscall_time_info(cpu);
    +
    rc = HYPERVISOR_vcpu_op(VCPUOP_up, cpu, NULL);
    BUG_ON(rc);

    diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
    index 0a5aa44..ab3119e 100644
    --- a/arch/x86/xen/time.c
    +++ b/arch/x86/xen/time.c
    @@ -474,6 +474,55 @@ void xen_timer_resume(void)
    }
    }

    +#ifdef CONFIG_PARAVIRT_CLOCK_VSYSCALL
    +void xen_setup_vcpu_vsyscall_time_info(int cpu)
    +{
    + int ret;
    + struct pvclock_vcpu_time_info *pvti;
    + struct vcpu_register_time_memory_area t;
    +
    + pvti = pvclock_get_vsyscall_time_info(cpu);
    + if (!pvti)
    + return;
    +
    + t.addr.pv = pvti;
    +
    + ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area,
    + cpu, &t);
    + /*
    + * If the call succeeds, it will update the vcpu_time_info and
    + * set the version to something valid. If it fails, we set
    + * the version to invalid so that usermode doesn't try to use
    + * it.
    + */
    + if (ret != 0)
    + pvti->version = ~0;
    +}
    +
    +static int __init xen_setup_vsyscall_timeinfo(int cpu)
    +{
    + int ret;
    +
    + ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area,
    + cpu, NULL);
    + if (ret == -ENOSYS) {
    + printk(KERN_INFO "xen: vcpu_time_info placement not supported\n");
    + return ret;
    + }
    +
    + ret = pvclock_init_vsyscall();
    + if (ret != 0) {
    + printk(KERN_INFO "xen: Failed to initialize pvclock vsyscall: %d\n",
    + ret);
    + return ret;
    + }
    +
    + xen_setup_vcpu_vsyscall_time_info(cpu);
    +
    + return 0;
    +}
    +#endif /* CONFIG_PARAVIRT_CLOCK_VSYSCALL */
    +
    __init void xen_time_init(void)
    {
    int cpu = smp_processor_id();
    @@ -496,4 +545,7 @@ __init void xen_time_init(void)

    xen_setup_timer(cpu);
    xen_setup_cpu_clockevents();
    +
    + if (xen_setup_vsyscall_timeinfo(cpu) == 0)
    + xen_clocksource.vread = pvclock_clocksource_vread;
    }
    diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
    index 22494fd..d92ddc8 100644
    --- a/arch/x86/xen/xen-ops.h
    +++ b/arch/x86/xen/xen-ops.h
    @@ -58,6 +58,14 @@ bool xen_vcpu_stolen(int vcpu);

    void xen_setup_vcpu_info_placement(void);

    +#ifdef CONFIG_XEN_TIME_VSYSCALL
    +void xen_setup_vcpu_vsyscall_time_info(int cpu);
    +#else
    +static inline void xen_setup_vcpu_vsyscall_time_info(int cpu)
    +{
    +}
    +#endif
    +
    #ifdef CONFIG_SMP
    void xen_smp_init(void);

    diff --git a/include/xen/interface/vcpu.h b/include/xen/interface/vcpu.h
    index 87e6f8a..0a8edfd 100644
    --- a/include/xen/interface/vcpu.h
    +++ b/include/xen/interface/vcpu.h
    @@ -170,4 +170,45 @@ struct vcpu_register_vcpu_info {
    };
    DEFINE_GUEST_HANDLE_STRUCT(vcpu_register_vcpu_info);

    +
    +/*
    + * Register a memory location to get a secondary copy of the vcpu time
    + * parameters. The master copy still exists as part of the vcpu
    + * shared memory area, and this secondary copy is updated whenever the
    + * master copy is updated.
    + *
    + * The intent is that this copy may be mapped (RO) into userspace so
    + * that usermode can compute system time using the time info and the
    + * tsc. Usermode will see an array of vcpu_time_info structures, one
    + * for each vcpu, and choose the right one by an existing mechanism
    + * which allows it to get the current vcpu number (such as via a
    + * segment limit). It can then apply the normal algorithm to compute
    + * system time from the tsc.
    + *
    + * However, because usermode threads are subject to two levels of
    + * scheduling (kernel scheduling of threads to vcpus, and Xen
    + * scheduling of vcpus to pcpus), we must make sure that the thread
    + * knows it has had a race with either (or both) of these two events.
    + * To allow this, the guest kernel updates the time_info version
    + * number when the vcpu does a context switch, so that usermode will
    + * always see a version number change when the parameters need to be
    + * revalidated. Xen makes sure that it always updates the guest's
    + * version rather than overwriting it. (It assumes that a vcpu will
    + * always update its own version number, so there are no cross-cpu
    + * synchronization issues; the only concern is that if the guest
    + * kernel gets preempted by Xen it doesn't revert the version number
    + * to an older value.)
    + *
    + * @extra_arg == pointer to vcpu_register_time_info_memory_area structure.
    + */
    +#define VCPUOP_register_vcpu_time_memory_area 13
    +
    +struct vcpu_register_time_memory_area {
    + union {
    + struct vcpu_time_info *v;
    + struct pvclock_vcpu_time_info *pv;
    + uint64_t p;
    + } addr;
    +};
    +
    #endif /* __XEN_PUBLIC_VCPU_H__ */
    --
    1.6.2.5


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